Cathode ray tube having a screen conforming to the peripheral surface of a cylinder



TATSUYA YAMADA ETAL CATHODE RAY TUBE HAVING A SCREEN CONFORMING TO THE PERIPHERAL SURFACE OF A CYLINDER 5 6 9 7. 1. w l 0 N w. a d M i J F Jan. 17, 1967 TAT$UYA 'YAMADA ETAL 3,299,314

CATHODE RAY TUBE HAVING A SCREEN CONFORMING TO THE PERIPHERAL SURFACE OF A CYLINDER Filed Dec. 12, 1963 4 Sheets-Sheet 3 F l G 4 4 Sheets-Sheet f4 FIG.I9

FIG

TATSUYA YAMADA ETAL CATHODE RAY'TUBE HAVING A SCREEN CONFORMING TO THE PERIPHERAL SURFACE OF A CYLINDER 12, 1963 F I G File Dec.

F 1 cf.

. 3,299,314 CATHODEQRAY TUBE HAVING A SCREEN CON- FORMING TO THE PERIPHERAL SURFACE OF A CYLINDER Tatsuya Yamada; Meguro-ku, Tokyo, Shin Hasegawa,

Kanagawa-ken, Yoshiaki .Nakayama, Setagaya-ku, Tokyo,.and Hidetada Neishi, Hodogaya-ku, Yokohamashi, Japan, assignors to Tokyo Shibaura Electric (30., Ltd., Kawasaki-shi, Japan, a corporation of Japan Filed Dec. 12, 1963, Ser. No. 330,077 Claims priority, application Japan, Dec. 29, 1962, 37/595241; Aug. 31, 1963, 38/46,20ll, 38/46,203, 38/415,209

19 Claims. (Cl. 315-25) This invention relates. to a cathode ray tube device and more particularly to a novel cathode ray tube device and an electron beam control system therefor comprising a flat envelope and an electron gun which is disposed substantially on one side of said envelope.

In conventional cathode ray tubes now widely utilized for televisions, radars and the like, funnel shaped envelopes have been used in most cases in which are disposed a fluorescent screen and an electron gun at right angle to and remote from said fluorescent screen in order to cause an electron beam to impinge upon said fluorescent screen so as to excite to luminescence. By such a construction, two deflecting systems which are disposed .orthogonally with each other along the path of the electron beam adjacent the electron gun are utilized to deflect the electron beam so as to scan the whole surface of the screen to produce images thereon. Thus these prior cathode ray tubes are advantageous in that the electron beam is caused to impinge upon the screen at high velocity, thus producing brilliant images, and that the beam can be easily deflected with small electric power consumption. However, such an arrangement in which the electron gun is disposed in opposite relation to and remote from the central portion of the screen requires large axial length of the electron gun, and funnel shaped envelope of large volume acting as the beam deflecting portion. Moreover, in order to produce still larger images it is necessary to use a funnel shaped envelope of larger axial length and hence of larger volume. Further, even when the electron gun is disposed closer to the screen so as to increase the degree of defiection, thus ultimately enabling a deflection of 180, it is necessary to project the electron gun rearward of the screen.

In order to obviate the above described disadvantages, that is to decrease the tube length as well as the volume of the funnel shaped portion on the rear side of the screen it has been attempted to deflect the electron beam so asto cause it to impinge upon the screen at right angle by sharply bending the axis of the electron beam at the junction with the funnel shaped portion or by arranging the axis of the electron beam in parallel with the screen but such arrangements require complicated conditions of beamfocusing, electrode arrangements and focusing and deflecting circuits. Thus, these arrangements are difiicult to manufacture, require excess bending of the beam, can not utilize high speed beams and can not produce bright images.

Accordingly the principal object of this invention is to provide cathode ray tubes in which the electron beam can be deflected very easily.

Another object of this invention is to provide flat cathode ray tubes having improved brightness.

Another object of this invention is to provide novel cathode ray tubes having smaller volume with regard to the screen area. I

Still another object of this invention is to provide United! States Patent Patented Jan. 17, 1967 cathode ray tubes having an extremely short axial length.

A further object of this invention is to provide a novel cathode ray tube, wherein the image thereof can be viewed both from front and rear sides.

A still further object of this invention is to provide novel cathode ray tubes which can operate with small beam-deflecting electric power for large screen area.

Another object of this invention is to provide an improved magnetic field device adapted to be incorporated with this cathode ray tube to facilitate the scanning operation of the electron beam.

The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The invention itself, however, as to its organization together with further objects and advantages ther of may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIG. 1 shows a perspective view of one embodiment of this invention illustrating a magnetic field device for beam alignment incorporated with a cathode ray tube;

FIG. 2 shows a front elevation of the device shown in FIG. 1;

FIG. 3 shows a longitudinal sectional view of the device shown in FIG. 1 taken along the line III-III and viewed in the direction indicated by arrows;

FIG. 4 is a diagram illustrating the principle of this invention;

FIG. 5 is a diagram helpful to explain a magnetic field device for beam alignment;

FIG. 6 shows a partially perspective view of one example of the magnetic field device;

FIG. 7 shows a longitudinal sectional view taken along the line VI-VI of FIG. 6 and viewed in the direction of arrows;

FIG. 8 is a plot showing the product of width and intensity of the magnetic field shown in FIG. 7;

FIG. 9 is a sectional view of a modified magnetic field device;

FIG. 10 is a plan view of the magnetic field device shown in FIG. 9 illustrating the field distribution thereof;

FIGS. 11 through 13 show plan views of still another modification of the magnetic field device;

. FIG. 14 is a diagrammatic view helpful in explaining the control system for an electron beam of a cathode ray tube embodying this invention;

FIGS. 15 and 16 are schematic cross sectional views taken along the line XV-XV and viewed in the direction of arrows and illustrate a first beam deflecting system incorporated therewith;

FIGS. 17 and 18 are similar cross sectional views to illustrate a second beam deflecting system used; and

FIG. 19 is a sectional view illustrating a third defleeting system.

Referring now to the accompanying drawings, in accordance with this invention a fiat cathode ray tube is provided as shown in FIG. 1. The cathode ray tube comprises an envelope 10 made of glass, for example, which includes a face plate portion 11 forming a part of a cylindrical surface, a transparent plate opposing said face plate portion to form a thin vessel, a funnel shaped portion 12 connected to one side of said hollow thin envelope and a neck portion 13 of reduced diameter and con nected to the neck of the funnel shaped portion.

Further, as shown in FIGS. 2 and 3, a fluorescent screen 14 is applied on the inner surface of the face plate 11 to form a curved surface conforming to a portion of the cylindrical surface just like the face plate 11. The neck portion 13 projects from one side of the fluorescent film 14 which is substantially parallel with the axis of the cylinder. The neck portion 13 is provided at one end there of with pins 15 of electrically conductive material and an electron gun 16 mounted in the neck. Within the funnel shaped portion 12, an electron beam a emitted from the electron gun toward the fluorescent film 14 is deflected as follows: In the embodiment shown, there are provided a first deflecting system 17 in the form of electrostatic plates and a second deflecting system 18 also in the form of electrostatic plates and disposed near the junction between the neck portion 13 and the funnel shaped portion 12. The latter deflecting system 18 functions to deflect the electron beam in the radial direction and cooperates with a beam alignment magnetic field device 19, to be described later, to scan the surface of the fluorescent film in a direction parallel to its cylinder axis. The inner surfaces of the face plate 11 and the transparent plate 20 opposite thereto are coated by transparent conductive films such as NESA films, for instance, so as to form an accelerating electrode 21. It is to be understood that the fluorescent film 14 is applied on the accelerating electrode 21. With this construction the fluorescent film 14 can be viewed both from its front and rear sides. Alternatively, at first a fluorescent film may be applied on the inner wall of the face plate and then coated with a metal back of thin metal layer of aluminium and the like. If desired, the accelerating electrode may be formed of any conductive film such as graphite and the like, in which case the fluorescent screen can be viewed from only one side thereof. Thus, the electron beam at emitted from the electron gun 16 in the neck portion 13 in a direction perpendicular to an imaginary cylinder axis of the surface of the fluorescent screen and directed obliquely to said surface is first deflected to the direction of the axis of the cylinder of the fluorescent screen, or normal to the sheet of the drawing (FIG. 3), by means of the second deflecting system 18 and is then deflected along the cylinder in a direction per pendicu'lar to the axis of the cylinder of the fluorescent screen 14, that is in the horizontal direction as viewed in the drawing by means of the first deflecting system, 17. However, as the electron beam is deflected in the radial direction by the action of the second deflecting system 18, at this stage the beam will trace a radial locus around said deflecting system so as to form a sector shaped raster on the fluorescent screen. The beam alignment magnetic field device 19 provides a magnetic field to prevent the above mentioned phenomena. Thus, the beam alignment magnetic field device 19 constitutes a collimator lens to impart to the electron beam a negative bias of the same angle of deflection to which the beam had been subjected by the action of the second deflecting system 18. Where the device 19 is formed by an electromagnet it should be energized to produce a reverse magnetic field with respect to the magnet center, which is proportional to the angle of deflection of the electron beam so as to cause it to scan over the entire surface of the fluorescent screen 14 in the direction of its cylindrical axis.

While the electron beam is additionally deflected by the action of the first deflecting system 17, as the beam impinges obliquely upon the fluorescent screen its angle of deflection can be made small with small deflecting power. The fluorescent spot will have a circular configuration due to oblique impingement of the electron beam upon the fluorescent screen. However, this can be corrected by so making the electron beam emitted from the electron gun as to have an oblong configuration in the axial direction of the cylinder of the fluorescent screen by arrangement of a well known means so as to form a circular fluorescent spot on the screen. Further, in the cathode ray tube constructed in accordance with this invention, the center 22 of the first deflecting system and the fluorescent screen 14 are on the same imaginary cylindrical surface so that the arcs of the scanning lines of the same length on the fluorescent screen 14 will subtend the same angle With respect to the deflection center 22. Accordingly if the electron beam were deflected horizontally at a uniform angular speed the electron beam spot would travel at a uniform speed on the horizontal plane of the fluorescent screen.

Thus, more particularly, reference is now to be had to FIG. 4 wherein it is assumed that an electron lens 23 formed by an electron gun, not shown in the drawing, is closely situated to the deflection center 22 of the first deflection system and that the deflected beam a impinges at an angle of incidence [3 upon a point S of the fluorescent screen 14 having a radius R. The diameter of the electron beam d, where the system is adjusted so that the spreading of the electron beam at the point S will be minimum, is proportional to the distance of travel of the beam after it has passed through the electron lens 23, provided that the effect of the space charge is ignored. Then following equation holds:

docZR sin {3 (1) Whereas, since the electron beam impinges at an angle ,8 upon the fluorescent screen 14, the major axis of the section thereof, that is the horizontal axis X of the electron beam spot will be given by X d/sin a (2) By eliminating the term d from the above Equations 1 and 2 the major axis X of the beam spot will become independent of the impinging angle B of the beam upon the fluorescent screen 14. Thus, the major axis X of the spot Will become constant irrespective to the location thereof on the fluorescent screen or a picture. However, in order to provide this effect it is necessary to use dynamic focusing, or to automatically adjust the focus of the electron lens 23 in accordance with the various portions scanned by the electron beam. This can be accomplished synchronously with horizontal deflection signals of saw teeth wave form.

As can be noted from the above description, with the cathode ray tube of this invention, distortionless scanning can be provided by utilizing a conventional saw tooth wave as the deflection signal without resorting to a corrected saw tooth wave. It is preferable to cause the electron beam emitted from the electron gun to pass through the center of the fluorescent screen before deflection.

It will be obvious to those skilled in the an that While in the above described embodiment the first and the second deflection systems 17 and 18 have been shown as electrostatic deflecting means, the electron beam can also be deflected electromagnetically by mounting deflecting coils upon the funnel shaped portion 12 and the neck portion 13. Thus, in the thin cathode ray tube of the present invention the electron beam is caused to scan across a fluorescent screen forming a part of a cylindrical surface in a direction perpendicular to the axis of a phantom cylinder along the equal peripheral surface thereof by means of a first deflecting system having its center of deflection on the same phantom cylindrical surface, so that the deflection of the electron beam can be effected easily and moreover the envelope can be constructed to have a thin configuration With an extremely short axial length and a small volume with regard to the screen area and can be operated With very small electric deflecting power.

Considering now a beam correcting magnetic field device by referring to FIG. 5, when the electron beam a is deflected in the axial direction of the cylinder of the fluorescent screen, or in the direction parallel to the direction of the sheet of drawing, by the action of the second deflecting system 18 the beam will be deflected in the radial direction within the funnel shaped portion. In order to bring the electron beam into parallel relation a magnetic field is provided for the shaded region F of FIG. 5 to deflect again the electron beam. This magnetic field may be provided by an electromagnet or a permanent magnet. For example, in a construction shown in FIGS. 6 and 7 the magnetic core 30 of the beam alignment magnetic field device 19 is shaped to have a rectangular configuration so that it can be fitted adjacent the junction between the face plate of the cathode ray tube and its funnel shaped portion so as to form a magnetic path to localize the magnetic flux only to a required sector. Each of the pairs of permanent magnets 31, 32 and 33, 34 of isosceles triangular configuration is securely mounted on theupper and lower inner surfaces of core 30 with their first apices abutting each other. Each of said permanent magnets 31* through 34 is uniformly magnetized in the direction of their thickness, and opposing magnets, that is magnets 31, 32, and 33, 34 are magnetized in opposite polarities so that lines of magnetic force produced by these magnets flow in the opposite direction on the opposite sides to the center of the length of the core 30,"as represented by broken'linesin FIG. 7. a 7

cathode ray tube through which the electron beam passes is substantially constant. Accordingly, when these magnets are paired as shown with their apices opposed, the Width of the magnetic field will coincide with that of the magnets 31 through 34, respectively. Thus as shown in FIG. 8, the product of the width and strength of the magnetic field will be zero at its center and have opposite polarities on both sides of the center 0, the absolute value of the field being substantially proportional to the distance. from said center.

, Because of this it will be easily understood that the above mentioned object can be attained by establishing the polarity of the magnetic field in the direction normal to the beam which has been deflected in the radial direction. :With the construction described, while it is possible to bring the electron beam into a substantially parallel relationship with the circumference of the fluorescent screen, if it is desired to more accurately establish the alignment of the beam, the following arrangement may be used:

It should be remembered that, where the angle of deflection from the second deflection center 24 of a flat cathode ray tube is large as shown in FIG. the product of the width and intensity of the magnetic field required in the region F of the magnetic field is zero at the center and has opposite polarities on the opposite sides thereof. But actually the product of the width and intensity of the magnetic field varies linearly near the center 0 but varies. non-linearly as the distance from the center increases, as shown by the dotted line of FIG. 8. For example, referring again to FIG. 5 the distance y between the point at which the electron beam a which is emitted from the deflection center 24 at a deflection angle a crosses the center line of the magnetic field F and the center 0 at which the product between the width and the strength of said magnetic field F is zero can be expressed as follows:

In order. to bring the beam into parallel relation with the circumferential direction of the fluorescent screen 14 or to change the direction of the beam a by an angle a after it has left the region of the magnetic field F, the following relation must be satisfied:

y=L tan a tan a=- ma eH 'By eliminating tan a and R from the above Equations 3 and 4,

mu 2 (L2 0H (5) amt) Ltd: J

H i-y where m, e, and v represent the mass, electric charge and speed of the electron, respectively.

Thus, strictly speaking, the relationship between the product of the width and intensity of the magnetic field with respect to the distance y from its center should satisfy the above Equation 6. Accordingly, in the region where the angle of' defiection is small as expressed by L y the product of the width d and the intensity H of the magnetic field is proportional to the distance y whereas as the angle of deflection increases, it is required to decrease IH-dl as indicated by the dotted lines of FIG. 8.

Accordingly in order to bring the radial beam into more accurate parallel relationship it is necessary to correct the configuration of the oblique sides of the magnets 31 through 34 shown in FIGS. 5 and 7 according to the dotted line shown in FIG. 8.

FIG. 9 of the accompanying drawing illustrates a modification of the beam correcting magnetic field device wherein the side plates 36 of the core 30 of the magnetic field device shown in FIGS. 6 and 7 are removed to alter the direction of the magnetic flux through the core 30. More particularly, the construction shown in FIG. 9 can prevent the tendency of weakening the magnetic field in the vicinity of the side plates 36 owing to the presence thereof. With the construction shown in FIG. 9, although the reluctance of the magnetic path of a loop 35 of the magnetic lines of force is twice that of the construction shown in FIG. 5, the strength of the magnetic field is not varied as the magneto-motive force is doubled. In this example it is advantageous to use nonmagnetic members corresponding to the side plates 36 so as to firmly secure in the desired spaced relationship the core 30 as well as magnets 31 and 34 inclusive. Alternatively, the core may be mounted directly upon the envelope of the cathode ray tube.

In the above embodiments, magnets of the regular isosceles triangular configuration are utilized as shown by FIG. 10. Referring to FIGS. 11 and 12, however, actually, with such plate magnets the lines of magnetic force in the space will fringe on both sides as shown by dotted lines 37 due to end effect and the like so that the point H max. of the strongest magnetic field strength will be shifted toward the center of the magnetic field device. More specifically, the point of H max. will be shifted to a point which is remote from the center by a distance from /2l to %l in our experiments; where l is the total length of one of the magnets. The region available for redefiecting the electron beam back so as to increase the total length of the magnetic field device is therefore limited. This tendency of increasing the length of the magnetic field device can be effectively prevented by shaping the plate magnets such that they abut one another at the center 0 with an acute angle and by concaving inwardly two sides subtending said angle so as to compensate the error due to end effect of the magnets and also to locate the point of H max. at a point more remote from the center 0 of the magnetic field device.

Furthermore, the electron beam can be made more uniformly parallel over the entire region of an electronic lens formed by the magnetic field device by shaping the magnets to have asymmetrical triangular configuration as shown in FIG. 13 so as to locate the point of strongest magnetic field on the outside of the electron beam a of the maximum deflection angle produced by the second deflection system having a deflection center 24, as shown in FIG. 5.

The magnets 31 through 34 may be flexible magnets such as rubber or plastic material containing powders of magnetic material, or the core 30 may be made of a suitable ferromagnetic material such as iron. Although in the drawing the plate magnets are shown with their apices abutting, since the lines of magnetic force have a tendency to fringe outwardly, best results can be obtained by cutting off a small portion of acute apices or spacing the apices at the center a little distance apart.

While it has been mentioned that the triangular plate magnets are uniformly magnetized over their entire surface, it is possible to weaken the field intensity at the center of the lens system and strengthen it towards the ends so as to make more effective to be used in this invention by partially varying the intensity of magnetization of the plate magnets, for instance by varying the intensity of the magnetizing force or by varying the contents of the magnetic material.

Furthermore, in accordance with this invention, a novel beam deflecting system suitable for decreasing the burden of redeflecting the electron beam of the above described beam alignment magnetic field device is provided. More particularly, as shown in FIG. 14, an electron beam at emitted from an electron gun 16 is first deflected in the radial direction by the action of the second deflecting system so as to scan across the surface of the fluorescent screen 14 forming a portion of a cylindrical surface in a direction parallel to the axis of said imaginary cylinder or in a direction perpendicular to the sheet of drawing and is then deflected along the periphery of said cylinder by the action of the first deflecting system in a direction perpendicular to the cylinder axis or in the horizontal direction as viewed in the drawing to arrive at the electron beam alignment magnetic field region F which constitutes an electronic lens. Thus, the electron beam will be redeflected in the reverse direction to provide correct horizontal scanning as shown by a line P-Q. Where the strength of the beam alignment magnetic field is smaller than the desired value the beam would not be sufficiently redeflected and assume a position indicated by a line PQ' so that the raster formed on the surface of the fluorescent screen will become trapezoidal.

As shown in FIG. 15, the first deflecting system comprises a pair of coils 17 and 17 which are asymmetrically mounted on the outer wall of the neck portion 13. The lines of magnetic force are produced by the coils as indicated by curved dotted lines 38 While the electron beam penetrates the sheet of the drawing from the front side to the rear side. The curves of the lines of the magnetic force are drawn in the following manner with respect to the fluorescent screen.

More particularly, the electron beam is deflected to scan in a direction perpendicular to the axis of the neck portion 13 by the action of the second deflecting system and then deflected in a direction perpendicular to lines MM' of FIG. 15 by the action of the first deflection system. Continuing the description, the beam arriving at a line interconnecting points p and q of the first deflecting system will impinge upon the portion of the fluorescent screen corresponding to a line which interconnects points P and Q and parallel with the axis of the neck portion, said line being shown in the upper portion of FIG. 14. In the same manner the electron beam arriving at a line which interconnects points p and q of the deflecting system 17 will impinge upon the fluorescent screen along a line which interconnects points P and Q.

In this case the electron beam which has passed through the portion of the first deflecting system 17 which is close to the fluorescent screen or the portion indicated by points p and q of FIG. 15 will be subjected to a deflecting force towards M. However, as already pointed out hereinabove, bending of the magnetic flux will produce a component in a direction perpendicular to a line M-M so that the electron beam will be deflected away from the center axis M-M' of the first deflecting system. Thus,

the beam will be subjected to the deflecting force in the same direction as the deflection caused by the sec-0nd deflecting system.

The electron beam passing through the portion represented by the line q-q of FIG. 15 will be subjected to a deflecting force in the direction of M so that the beam will be subjected to a deflecting force toward the center axis M-M' under the influence of a magnetic flux, similarly curved but in the opposite direction as that of the above case. Thus, the deflecting force will act to decrease the angle of deflection caused by the second deflecting system.

As stated hereinbefore, since the deflection angle caused by the second deflection system is corrected by the first deflecting system in accordance with the deflection angle thereof it is not necessary to use an especially strong magnetic field for the magnetic field region F or the collimator electronic lens but the magnetic field may be of a weak intensity sufl'lcient to correct the beam deflection angle. In some cases, the collimator electronic lens may be eliminated.

While in the above illustrated embodiment, deflecting coils have been used in the first deflecting system 17, the same object can be attained by employing an electrostatic system wherein the first deflecting system is constituted by a pair of curved deflecting plates 17 and 17 as shown in FIG. 16. Corresponding parts of FIGS. 15 and 16 are designated by the same reference numerals, excepting the numeral 38' which indicates an equipotential surface.

As Will be obvious from the above description use of the first deflecting system eliminates the necessity of using a collimator electronic lens of especially strong magnetic field. Even when such an electronic lens is eliminated it is able to provide a regular rectangular raster on the fluorescent screen, thus providing a novel flat cathode ray tube characterized by improved tube characteristics.

The above mentioned correction may similarly be made by the second deflecting system. Thus as shown in FIG. 17 there are mounted upon the outer Wall of the neck portion 13 a pair of deflecting coils 18 and 18 adapted to scan the electron beam in a direction perpendicular to the fluorescent screen as viewed in FIG. 14. As shown by their section in FIG. 17 these deflecting coils are constructed such that in a plane perpendicular to the direction of travel of the beam, the magnetic field is stronger (i.e. the flux density is higher) on the side p of the neck portion near the fluorescent screen whereas the magnetic field is weaker on the opposite side. The broken line in FIG. 17 indicates the line of magnetic force.

Accordingly, the electron beam emitted from the electron gun is deflected in a direction perpendicular to the fluorescent screen 14 by the action of a conventional horizontal deflecting system which is disposed closer to the electron gun than the second deflection system and then the beam arrives at the vertical deflection coils 18 and 18 scanned between points p and q of the drawing. The electron beam which passes through the point 1 will impinge upon the portion P-P of the fluorescent screen 14, FIG. 14, which is close to the funnel shaped portion 12, while the electron beam that passes through the point q will impinge upon the portion QQ" of the fluorescent screen. In this case since the intensity of magnetic field at the point p is stronger than that at the point q of the deflection coils 18 and 18 the deflection angle u when the beam impinges upon the point P is larger than the deflecting angle when the beam impinges upon the point Q, Where one of the scanning lines, for example P-Q of the fluorescent screen 14 is scanned. The deflecting angle will vary continuously between angles u and a when the beam scans between the points P and Q. With such a design, within the beam alignment magnetic field region F. the beam is required to be deflected slightly, i.e., only enough to correct the beam, so that sufficiently weak magnetic field may be used. If the As the result, at this portion the beam is being beam deflection angle can be controlled only by deflection coils 18 and 18 so as to produce scanning lines which are parallel with the horizontal direction of the fluorescent screen the beam alignment magnetic field device may be omitted. Further if the deflecting coils 18 and 18 are so designed that the intensity of the magnetic field varies continuously between points p and q contained in their cross section, it is able to use a deflecting current which has been utilized heretofore to produce uniform magnetic field.

When a conventional vertical deflecting coil which produces a parallel magnetic flux is utilized the electron beam will be subjected only to the deflection force in the vertical direction in any portion of the magnetic field produced by said deflecting coil. However the magnetic flux produced by the deflection coils of this example is not a parallel flux as indicated by the broken line 39 of FIG. 17.

With the vertical deflecting coils constructed in accordance with this invention, the deflecting force includes a horizontal component as shown by arrows B in FIG. 17 so that the starting and end points of the raster will approach the electron gun where the vertical deflection angle is large. Accordingly the raster will have a configuration projecting toward the electron gun with its apex at the horizontal center portion.

However, this can be easily corrected by superposing a frequency component which is the same as the vertical deflection frequency, upon the horizontal deflection voltageor current.

I In order to obtain a deflecting coil which produces nonparallel magnetic flux, two coils having different sizes may be used in a pair or two equal coils may be used in combination. with pole pieces of different material or different dimensions. Alternatively, the above objective can be attained by varying the relative magnitude of the currents flowing through identical coils. In any case the coils should be designed to produce a continuously varying magnetic field which is denser on one side of the cross section than on the other side.

While in the above description the second deflecting system has been shown as coils, any suitable electrostatic deflecting device can be used instead of coils as has been pointed out in connection with the first deflecting system. Thus, for example, as shown in FIG. 18, a pair of opposing deflecting plates 18; and 18 may be disposed such that the distance between them varies between both sides p and q.

, Although, in the above embodiments, the first deflecting system is situated between the second deflecting system and the electron gun, actually, as each deflecting system has substantial axial length both deflecting systems may besuperposed upon one another so that they may have a common deflection center.

As will be obvious from the foregoing description this invention can provide a novel flat cathode ray tube device of improved characteristic wherein a raster of regular rectangular configuration can be provided on the fluorescent screen without using any collimator electronic lens of particularly strong magnetic field. If desired such deflecting systems or collimator electronic lens may be dispensed with.

While in the above described embodiments an electron beam for scanning was corrected by the action of fields generated by a first and a second deflecting systems, the same object can be attained by utilizing a third deflecting system which generates a fixed field in addition to said first and second deflecting systems.

For example, as shown in FIG. 19, there is provided a third deflecting system of the electrostatic type including a pair of opposing electrodes 40, and 40 having such a configuration as, to establish a barrel shaped equipotential surface 41. When a positive potential is impressed upon the electrode 40 which is closer to the fluorescent screen, the electron beam that passes across the portion p-p will be deflected at a larger angle toward the cylinder axis of the fluorescent screen whereas the electron beam that passes across the portion q-q' will be subjected to opposite action thus easily forming a rectangular or square raster. Thus the additional deflecting system is of such dimension that the intensity of the static field established thereby is relatively weak near the path of the nondeflected electron beam but relatively strong near the path of the beam, through which it passes when deflected by the second deflecting system, or the strength of the field increases in the direction toward the cylinder axis of the fluorescent screen.

Thus, the essential feature of this invention is to provide a cathode ray tube comprising a fluorescent screen forming a portion of a cylinder and a deflecting system having a deflection center on the same imaginary cylinder as said screen. By this invention it is not only possible to form the envelope of the cathode ray tube as a thin member having a face plate on which is coated a screen as one side of the envelope but also a neck portion housing an electron gun can project from another side of the envelope so as to form a thin cathode ray tube. Moreover, inasmuch as the cathode ray tube produces a rectangular raster by incorporating means to vary the intensity of the field at various positions of the electron beam or a third deflecting system of the electrostatic type having fixed field intensity wtih an electron beam alignment magnetic field which forms a collimator electronic lens and/ or a first and second deflecting systems which serve to deflect the electron beam in two different directions, a very effective electron beam control system can be provided.

In accordance with the provisions of the patent statutes, we have explained the principle and operation of our invention and have illustrated and described what we consider to represent the best embodiments thereof. However, we desire to have it understood that Within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

What we claim is: t

1. A cathode ray tube comprising -a thin exhausted envelope including one surface comprised by a face plate which forms a portion of the peripheral surface of a cylinder, said face plate having a coating of a fluorescent screen applied to the inner surface thereof, a funnel shaped portion formed on one side of said envelope, and a neck portion connected to the outer end of said funnel shaped portion and enclosing therein an electron gun which emits an electron beam; and a plurality of deflecting systems for deflecting said electron beam, one of said deflect'mg systems having its deflection center in a plane which is essentially a continuation of the inner surface of said face plate and said thin envelope being formed of a transparent material so as to enable .said fluorescent screen to be viewed from both sides thereof.

2. A cathode ray tube comprising a fluorescent screen conforming to a portion of the peripheral surface of a cylinder, an electron gun adapted to direct an electron beam in a direction perpendicular to the axis of said cylinder and at an angle with respect to the surface of said fluorescent screen and at least one deflecting system to deflect said electron beam and cause it to scan the surface of said screen, one of said deflecting systems having its deflection center on the surface of a cylinder which is substantially the same as said screen.

3. The cathode ray tube according to claim 2, wherein the cross-section of the electron beam emitted from said electron gun is made to have an elongated shape in the axial direction of said cylinder.

4. The cathode ray tube device according to claim 2 wherein said first and second deflecting systems have common deflection center.

5. The cathode ray tube according to claim 2 wherein said electron beam which is emitted from said electron gun and passes through the deflection system is caused to impinge upon the center of said fluorescent screen.

6. A cathode ray tube comprising a fluorescent screen 1 l conforming to a portion of the peripheral surface of a cylinder, an electron gun adapted to direct an electron beam in a direction perpendicular to the axis of said cylinder and at an angle with respect to the surface of said fluorescent screen and at least a first and a second deflecting systems for deflecting said electron beam in mutually perpendicular directions, said first deflecting system having its deflection center on the surface of a cylinder which is substantially the same as said screen for scanning said electron beam along the cylindrical surface including said screen in a direction er endicular to the axis of said cylinder and said second deflecting system serving to deflect said electron beam in a direction parallel to the axis of said cylinder.

7. The cathode ray tube device according to claim 6 wherein said first deflecting system contributes to horizontal scanning of said electron beam and said second deflecting system to the vertical scanning of said electron beam.

8. The cathode ray tube according to claim 6 wherein said electron gun, said second deflecting system and said first deflecting system are disposed along the path of travel of said electron beam in the order mentioned and the lines of magnetic force or an equipotential surface created by said first deflecting system are convexed toward said fluorescent screen.

9. The cathode ray tube according to claim 6 wherein said electron gun, said first deflecting system and said second deflecting system are disposed along the path of travel of said electron beam in the order mentioned and the intensity of the field created by said second deflecting system in a plane normal to said path of travel of said electron beam is made stronger on the side close to said fluorescent screen and weaker on the side remote there from.

10. The cathode ray tube device according to claim 6 wherein there is provided a third deflecting system which establishes a static field which is weaker at a point through which the beam passes when nondeflected and becomes stronger at points located remote from said first mentioned point through which the beam passes after deflected by said second deflecting system.

11. The cathode ray tube device according to claim 6 wherein said first and second deflecting systems have common deflection center.

12. The cathode ray tube according to claim 6 wherein said electron beam which is emitted from said electron gun and passes through the deflection system is caused to impinge upon the center of said fluorescent screen.

13. A cathode ray tube device comprising an image displaying screen conforming with a portion of the peripheral surface of a cylinder, an electron gun for directing an electron beam in a direction perpendicular to the axis of said cylinder and at an angle with respect to said screen, a first and second deflecting systems for deflecting said electron beam in mutually perpendicular directions, and a magnetic field generating means to establish band shaped magnetic field across said electron beam for redeflecting said deflected electron by a predetermined angle dependent upon the deflection of said beam, the product of the width and intensity of said magnetic field being zero at its center and the absolute value of said product increasing in opposite directions in proportion to the distance from said center, said first deflecting system having its deflection center on the surface of a cylinder which is substantially the same as said screen for scanning said electron beam along the peripheral surface of said screen in a direction perpendicular to the axis thereof, said deflecting system deflecting radially said electron beam, said magnetic field generating means collimating said radially deflected electron beam and said second deflecting system and said magnetic field generating means cooperating to cause said electron beam to scan the surface of said screen in the axial direction of said cylinder whereby to draw a raster.

14. The cathode ray tube according to claim 13 wherein said first deflecting system contributes to horizontal scanning of said electron beam and said second deflecting system to the vertical scanning of said electron beam.

15. The cathode ray tube device according to claim 13 wherein there is provided a third deflecting system which establishes a static field which is weaker at a point through which the beam passes when nondeflected and becomes stronger at points located remote from said first mentioned point through which the beam passes after deflected by said second deflecting system.

16. The cathode ray tube according to claim 13 wherein the cross-section of the electron beam emitted from said electron gun is made to have an elongated shape in the axial direction of said cylinder.

17. In a beam alignment magnetic field device for a cathode ray tube including a magnetic field generating device for establishing a band shaped magnetic field across an electron beam emitted from an electron gun of said cathode ray tube in a line form and deflected into a flat radial form by means of a deflecting system, and then redeflecting said electron beam by a predetermined angle dependent upon the deflection of said beam so that the product of the width and intensity of said magnetic field is zero at its center and the absolute value of said product increasing in opposite directions substantially in proportion to the distance from the center, the improvement therein wherein said beam alignment magnetic device includes four plate magnets of identical configuration, each of which being substantially of an isosceles triangular configuration and magnetized in the direction of the thickness thereof, means to symmetrically arrange said plate magnets in two pairs each including two magnets with their first apices opposing each other, means to hold said magnet pairs with the faces of the respective pair opposing each other and with their polarities opposite and a core provided outside of said plate magnets to form a magnetic path for localizing the magnetic flux generated to the required space.

18. The beam alignment magnetic field device according to claim 17 wherein said core holds said plate magnets.

19. The beam alignment magnetic field device according to claim 17 wherein two sides subtending an acute angle formed at each of the first apices of triangles comprised by four plate magnets are concaved inwardly so as to correct an error caused by the end effect of said magnets and the point of maximum field intensity is located at a point as far as possible from said first apex measured in the longitudinal direction.

References Cited by the Examiner UNITED STATES PATENTS 2,498,354 2/1950 Bocciarelli 3l7200 X ROBERT L. GRIFFIN, Acting Primary Examiner.

T. A. GALLAGHER, Assistant Examiner. 

1. A CATHODE RAY TUBE COMPRISING A THIN EXHAUSTED ENVELOPE INCLUDING ONE SURFACE COMPRISED BY A FACE PLATE WHICH FORMS A PORTION OF THE PERIPHERAL SURFACE OF A CYLINDER, SAID FACE PLATE HAVING A COATING OF A FLUORESCENT SCREEN APPLIED TO THE INNER SURFACE THEREOF, A FUNNEL SHAPED PORTION FORMED ON ONE SIDE OF SAID ENVELOPE, AND A NECK PORTION CONNECTED TO THE OUTER END OF SAID FUNNEL SHAPED PORTION AND ENCLOSING THEREIN AN ELECTRON GUN WHICH EMITS AN ELECTRON BEAM; AND A PLURALITY OF DEFLECTING SYSTEMS FOR DEFLECTING SAID ELECTRON BEAM, ONE OF SAID DEFLECTING SYSTEMS HAVING ITS DEFLECTION CENTER IN A PLANE WHICH IS ESSENTIALLY A CONTINUATION OF THE INNER SURFACE OF SAID FACE PLATE AND SAID THIN ENVELOPE BEING FORMED OF A TRANSPARENT MATERIAL SO AS TO ENABLE SAID FLUORESCENT SCREEN TO BE VIEWED FROM BOTH SIDES THEREOF. 